An extensive flow cytometric evaluation continues of patients with autoimmune lymphoproliferative syndrome (ALPS) and their extended family membershasw established expanded double-negative T-cell and B-cell populations. Double-negative T-cells have been demonstrated to be alpha beta TcR, CD57+, HLA-DR+, and CD45RA+. This study has been extended to characterize the double-negative T-cells more completely including B220 expression and gamma-delta TcR T-cells in all ALPS patients. In addition, B cells have been found to have dimished memory B cells based on a decreased level of CD27 expression accompanied by altered repertoire of immunoglobuine heavy chain expression and an expansion of CD5+ B cells. Immunoregulatory T cell appear to be present in normal numbers based on a quantitiative RTPCR assay for Fox P3 and normal intracellular Fox P3 staining by flow cytometry despite the depression CD4/CD25 T cells. We have thus turned to the microarray results from B cell lines obtained from ALPS patients and mutation positive family members without disease to evaluate possible genetic links to disease development. These studies are early in development and at present no genetic basis for disease development has been identified in the setting of Fas gene mutations (ALPS type 1a patients). In addition, we have identified increased levels of vitamin B12 are found in ALPS patients along with the previous observation of increased levels of plasma IL-10 in ALPS patients. Finally, many of the symptomatic ALPS patients have eosinophilia and monocytopenia. At the present time we are performing a longitudinal assessment of all altered laboratory studies and comparing these to the clinical phenotype and genotype of all ALPS patients to identify the optimal screening lab tests for ALPS.